Abrasive, abrasive set, and method for abrading substrate

ABSTRACT

The polishing agent of the invention comprises water, an abrasive grain containing a hydroxide of a tetravalent metal element, and a specific glycerin compound.

TECHNICAL FIELD

The present invention relates to a polishing agent, a polishing agentset and a polishing method for a base substrate using the polishingagent or the polishing agent set. In particular, the invention relatesto a polishing agent and polishing agent set to be used in a flatteningstep of a base substrate surface as a production technique for asemiconductor element, and to a polishing method for a base substrateusing the polishing agent or the polishing agent set. More specifically,the invention relates to a polishing agent and polishing agent set to beused in a flattening step for a Shallow Trench Isolation (hereunder,“STI”) insulating material, a pre-metal insulating material or aninterlayer insulating material, and to a polishing method for a basesubstrate using the polishing agent or the polishing agent set.

BACKGROUND ART

In recent years, processing techniques for increasing density andmicronization are becoming ever more important in manufacturing stepsfor semiconductor elements. One such machining technique, CMP (chemicalmechanical polishing) technique, has become an essential technique inmanufacturing steps for semiconductor elements, for STI formation,flattening of pre-metal insulating materials or interlayer insulatingmaterials, and formation of plugs or embedded metal wirings, and thelike.

Most commonly used as CMP polishing agents are silica-based CMPpolishing agents containing silica (silicon oxide) particles such asfumed silica and colloidal silica as abrasive grains. Silica-based CMPpolishing agents have a feature of high flexibility of use, andappropriate selection of the abrasive grain content, pH and additivesallows polishing of a wide variety of materials regardless of theinsulating material or the conductive material.

Demand is also increasing for CMP polishing agents comprising ceriumcompound particles as abrasive grains, mainly designed for polishing ofinsulating materials such as silicon oxide. For example, ceriumoxide-based CMP polishing agents comprising cerium oxide (ceria)particles as abrasive grains allow the polishing of silicon oxide athigh rate, with even lower abrasive grain contents than silica-based CMPpolishing agents (see Patent Literatures 1 and 2, for example).

Addition of various organic compounds to polishing agents is known foradjusting the polishing properties of polishing agents. For example,addition of surfactants to cerium oxide-based CMP polishing agents isknown. As such techniques, the polishing agent comprising a nonionicsurfactant having HLB value of 17.5 or greater (such as polyoxypropyleneglyceryl ether) is known (see Patent Literature 3, for example).

Recently, as demand increases for achieving greater micronization ofwirings in manufacturing steps for semiconductor elements, generation ofpolishing scratches during polishing are becoming problematic.Specifically, even when fine polishing scratches generates during thepolishing using conventional cerium oxide-based polishing agents, it wasnot problematic so long as the sizes of the polishing scratches aresmaller than conventional wiring widths, but it can be problematic evenwhen the polishing scratches are fine for achieving further greatermicronization of wirings.

A solution to this problem is being sought through studying polishingagents that employ particles of hydroxides of a tetravalent metalelement (see Patent Literature 4, for example). Methods for producingparticles of hydroxides of a tetravalent metal element are also beingstudied (see Patent Literature 5, for example). Such techniques areaimed at reducing particle-induced polishing scratches, by maintainingthe chemical action of particles of the hydroxide of a tetravalent metalelement while minimizing their mechanical action.

CITATION LIST Patent Literature

-   [Patent Literature 1] Japanese Unexamined Patent Application    Publication HEI No. 10-106994-   [Patent Literature 2] Japanese Unexamined Patent Application    Publication HEI No. 08-022970-   [Patent Literature 3] Japanese Unexamined Patent Application    Publication No. 2009-212378-   [Patent Literature 4] International Patent Publication No.    WO2002/067309-   [Patent Literature 5] Japanese Unexamined Patent Application    Publication No. 2006-249129

Non-Patent Literature

-   [Non-Patent Literature 1] Complete Works of Dispersion Technology,    Johokiko Co., Ltd., July, 2005, Chapter 3, “Dispersers: Recent    development trends and selection criteria”

SUMMARY OF INVENTION Technical Problem

However, while the techniques described in Patent Literatures 4 and 5reduce polishing scratches, they cannot be said to provide sufficientlyhigh polishing rate for insulating materials. Since polishing rateaffects the efficiency of the production process, polishing agents withhigher polishing rates are desired.

Furthermore, in CMP steps for formation of STIs, insulating materialssuch as silicon oxide are polished using silicon nitride, polysilicon orthe like as stopper materials (constituent materials of polish stoplayers). In such cases, there is a need for a polishing agent with highpolishing selectivity for insulating material with respect to stoppermaterial (polishing rate ratio: polishing rate of insulatingmaterial/polishing rate of stopper material), in order to improveflatness and minimize erosion (overpolishing of the stopper material).

It is an object of the present invention to solve this technical problemand provide a polishing agent, a polishing agent set and a polishingmethod that can increase the polishing rate for insulating materials andthat can also improve the polishing selectivity for insulating materialswith respect to stopper materials.

Solution to Problem

In conducting research on increasing interaction between abrasive grainsand insulating materials with the aim of solving the problem describedabove, the present inventors conceived bridging abrasive grains andinsulating materials with hydrogen bonding by specific glycerincompounds, and has completed the invention.

The polishing agent according to the first embodiment of the inventioncomprises water, an abrasive grain containing a hydroxide of atetravalent metal element, and a glycerin compound, the glycerincompound being at least one selected from the group consisting ofcompounds represented by general formula (I) below and compoundsrepresented by general formula (II) below.[Chemical Formula 1]HO

C₃H₅(OH)—O

_(m)H  (I)

[In formula (I), m is an integer of 3 or greater.]

[In formula (II), n represents an integer of 2 or greater, and R¹, R²and the multiple R³ each independently represent hydrogen atom, a grouprepresented by general formula (III) below or a group represented bygeneral formula (IV) below. The case where R¹, R² and the multiple R³are all hydrogen atom is excluded.]

[In formula (III), p represents an integer of 1 or greater.]

[In formula (IV), q represents an integer of 1 or greater.]

With the polishing agent according to the first embodiment of theinvention, it is possible to increase the polishing rate for insulatingmaterials while also improving polishing selectivity for insulatingmaterials with respect to stopper materials, compared to a conventionalpolishing agent. Also, with the polishing agent according to the firstembodiment of the invention, in CMP techniques for flattening of STIinsulating materials, pre-metal insulating materials, interlayerinsulating materials and the like, it is possible to polish theseinsulating materials at high rate while also improving the polishingselectivity for insulating materials with respect to stopper materials.In addition, the polishing agent according to the first embodiment ofthe invention can allow the polishing of insulating materials with lowpolishing scratches while also increasing the polishing rate forinsulating materials.

The polishing agent according to the second embodiment of the inventioncomprises water, an abrasive grain containing a hydroxide of atetravalent metal element, and a glycerin compound, the glycerincompound being at least one selected from the group consisting ofpolyglycerin, diglycerin derivatives and polyglycerin derivatives, andthe HLB (Hydrophile-Lipophile Balance) value of the glycerin compoundbeing 19.8 to 20.0.

Throughout the present specification, “polyglycerin” refers topolyglycerin having a glycerin mean polymerization degree of 3 orgreater (polyglycerin that is a trimer or more). Also, throughout thepresent specification, “diglycerin derivative” refers to a compoundhaving a functional group introduced into diglycerin, and “polyglycerinderivative” refers to a compound having a functional group introducedinto polyglycerin that has a glycerin mean polymerization degree of 3 orgreater.

With the polishing agent according to the second embodiment of theinvention, it is possible to increase the polishing rate for insulatingmaterials while also improving polishing selectivity for insulatingmaterials with respect to stopper materials, compared to a conventionalpolishing agent. Also, with the polishing agent according to the secondembodiment of the invention, in CMP techniques for flattening of STIinsulating materials, pre-metal insulating materials, interlayerinsulating materials and the like, it is possible to polish theseinsulating materials at high rate while also improving the polishingselectivity for insulating materials with respect to stopper materials.In addition, the polishing agent according to the second embodiment ofthe invention can allow the polishing of insulating materials with lowpolishing scratches while also increasing the polishing rate forinsulating materials.

In the polishing agent according to the second embodiment of theinvention, the glycerin compound may be a polyoxyalkylene diglycerylether, and it may be a polyoxyalkylene polyglyceryl ether. This canfurther increase the polishing rate for insulating materials while alsofurther improving polishing selectivity for insulating materials withrespect to stopper materials.

In the polishing agent of the invention, the hydroxide of a tetravalentmetal element is preferably at least one selected from the groupconsisting of hydroxide of rare earth metal element and hydroxide ofzirconium. This can further increase the polishing rate for insulatingmaterials while also further improving polishing selectivity forinsulating materials with respect to stopper materials.

The mean particle diameter of the abrasive grain is preferably 1 nm orgreater and 300 nm or less. This can further increase the polishing ratefor insulating materials while also further improving polishingselectivity for insulating materials with respect to stopper materials.

The content of the abrasive grain is preferably 0.005 mass % or greaterand 20 mass % or less based on the total mass of the polishing agent.This can further increase the polishing rate for insulating materialswhile also further improving polishing selectivity for insulatingmaterials with respect to stopper materials.

The weight-average molecular weight of the glycerin compound ispreferably 250 or greater and 10×10³ or less. This can further increasethe polishing rate for insulating materials while also further improvingpolishing selectivity for insulating materials with respect to stoppermaterials.

The content of the glycerin compound is preferably 0.01 mass % orgreater and 10 mass % or less based on the total mass of the polishingagent. This can further increase the polishing rate for insulatingmaterials while also further improving polishing selectivity forinsulating materials with respect to stopper materials.

The pH of the polishing agent of the invention is preferably 3.0 orgreater and 12.0 or less. This can further increase the polishing ratefor insulating materials while also further improving polishingselectivity for insulating materials with respect to stopper materials.

One aspect of the invention relates to the use of the aforementionedpolishing agent in a polishing method for polishing of a surface to bepolished containing silicon oxide. That is, the polishing agent of theinvention is preferably used for polishing of the surface to be polishedcontaining silicon oxide.

The polishing agent set of the invention comprises constituentcomponents of the polishing agent separately stored as a first liquidand a second liquid, the first liquid containing the abrasive grain andwater, and the second liquid containing the glycerin compound and water.The polishing agent set of the invention can increase the polishing ratefor insulating materials while also improving polishing selectivity forinsulating materials with respect to stopper materials, compared to thecase using a conventional polishing agent.

The polishing method for a base substrate according to a firstembodiment of the invention may comprise a step of polishing the surfaceto be polished of a base substrate using the aforementioned polishingagent, or it may comprise a step of polishing the surface to be polishedof a base substrate using a polishing agent obtained by mixing the firstliquid and the second liquid of the aforementioned polishing agent set.According to these polishing methods, by using the aforementionedpolishing agent or polishing agent set, it is possible to increase thepolishing rate for insulating materials while also improving polishingselectivity for insulating materials with respect to stopper materials,compared to the case using a conventional polishing agent. Also,according to these polishing methods, it is possible to minimizeoccurrence of dishing while also improving the polishing selectivity forinsulating materials with respect to stopper materials.

Also, the polishing method for a base substrate according to a secondembodiment of the invention is a polishing method for a base substratehaving an insulating material and polysilicon, where the polishingmethod may comprise a step of selectively polishing the insulatingmaterial with respect to the polysilicon using the aforementionedpolishing agent, or it may comprise a step of selectively polishing theinsulating material with respect to the polysilicon using a polishingagent obtained by mixing the first liquid and the second liquid of theaforementioned polishing agent set. According to these polishingmethods, by using the aforementioned polishing agent or polishing agentset, it is possible to increase the polishing rate for insulatingmaterials while also improving polishing selectivity for insulatingmaterials with respect to polysilicon, compared to the case using aconventional polishing agent. Also, according to these polishingmethods, it is possible to minimize occurrence of dishing while alsoimproving the polishing selectivity for insulating materials withrespect to polysilicon.

Advantageous Effects of Invention

According to the invention, it is possible to provide a polishing agent,a polishing agent set and a polishing method that can increase thepolishing rate for insulating materials and that can also improve thepolishing selectivity for insulating materials with respect to stoppermaterials. According to the invention, it is possible to provide apolishing agent, a polishing agent set and a polishing method that canincrease the polishing rate for insulating materials and that can alsoimprove the polishing selectivity for insulating materials with respectto stopper materials, during the polishing of insulating materials usingstoppers. Furthermore, according to the invention, particularly, in CMPtechniques for flattening of STI insulating materials, pre-metalinsulating materials, interlayer insulating materials and the like, itis possible to provide a polishing agent, a polishing agent set and apolishing method that can polish these insulating materials at high rateand that can also improve the polishing selectivity for insulatingmaterials with respect to stopper materials. In addition, according tothe invention, it is possible to allow the polishing of insulatingmaterials with low polishing scratches while also increasing thepolishing rate for insulating materials.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing the aggregated condition ofabrasive grains when an additive has been added.

FIG. 2 is a schematic diagram showing the aggregated condition ofabrasive grains when an additive has been added.

DESCRIPTION OF EMBODIMENTS

The polishing agent, the polishing agent set and the polishing methodfor a base substrate using the polishing agent or the polishing agentset, according to an embodiment of the invention, will now be explainedin detail.

The polishing agent of this embodiment is a composition that contactswith a surface to be polished during polishing, and it is a CMPpolishing agent, for example. Specifically, the polishing agent of thisembodiment comprises at least water, abrasive grains containing ahydroxide of a tetravalent metal element, and a specific glycerincompound. The essential components and optionally added components willnow be described.

(Abrasive Grains)

The abrasive grains contain a hydroxide of a tetravalent metal element.Throughout the present specification, the term “hydroxide of atetravalent metal element” refers to a compound containing a tetravalentmetal (M⁴⁺) and at least one hydroxide ion (OH⁻). The hydroxide of atetravalent metal element may contain an anion other than a hydroxideion (for example, a nitrate ion NO₃ ⁻ and sulfate ion SO₄ ²⁻). Forexample, the hydroxide of a tetravalent metal element may contain ananion (for example, a nitrate ion NO₃ ⁻ and sulfate ion SO₄ ²⁻) bondedto a tetravalent metal element.

Abrasive grains containing a hydroxide of a tetravalent metal elementhave high reactivity with insulating materials (such as silicon oxide)compared to conventional abrasive grains composed of silica, ceria orthe like, and are able to polish insulating materials at high polishingrates. In a polishing agent according to this embodiment, other abrasivegrains may be used in addition to abrasive grains containing a hydroxideof a tetravalent metal element. Such other abrasive grains may be, forexample, particles of silica, alumina, ceria or the like. Also,composite particles containing a hydroxide of a tetravalent metalelement and silica may be used as the abrasive grains containing ahydroxide of a tetravalent metal element.

For the abrasive grains, the content of the hydroxide of a tetravalentmetal element is preferably 80 mass % or greater, more preferably 90mass % or greater, even more preferably 95 mass % or greater, especiallypreferably 98 mass % or greater and extremely preferably 99 mass % orgreater, based on the total abrasive grains. From the viewpoint of moreexcellent polishing properties as well as easier preparation of thepolishing agent, it is most preferred for the abrasive grains to becomposed of a hydroxide of a tetravalent metal element (i.e. 100 mass %of the abrasive grains consists of particles of the hydroxide of atetravalent metal element).

The hydroxide of a tetravalent metal element is preferably at least oneselected from the group consisting of hydroxide of rare earth metalelement and hydroxide of zirconium. The hydroxide of a tetravalent metalelement is preferably a hydroxide of rare earth metal element, from theviewpoint of further increasing the polishing rate for insulatingmaterials. Rare earth metal elements that can adopt tetravalent formsinclude lanthanoids such as cerium, praseodymium and terbium, amongwhich lanthanoids are preferred and cerium is more preferred from theviewpoint of a more excellent polishing rate for insulating materials. Ahydroxide of rare earth metal element and hydroxide of zirconium may beused in combination, or two or more may be selected for use from amonghydroxides of rare earth metal element.

The lower limit for the mean particle diameter of the abrasive grains inthe polishing agent or the slurry of the polishing agent set describedhereunder is preferably 1 nm or greater, more preferably 2 nm or greaterand even more preferably 3 nm or greater, from the viewpoint of furtherincreasing the polishing rate for insulating materials. The upper limitfor the mean particle diameter of the abrasive grains is preferably 300nm or less, more preferably 250 nm or less, even more preferably 200 nmor less, especially preferably 100 nm or less and extremely preferably50 nm or less, from the viewpoint of further minimizing scratches at thesurface to be polished. From these viewpoints, the mean particlediameter of the abrasive grains is more preferably 1 nm or greater and300 nm or less.

The “mean particle diameter” of the abrasive grains is the meansecondary particle size of the abrasive grains. For example, the meanparticle diameter of the abrasive grains can be measured for thepolishing agent or the slurry of the polishing agent set describedhereunder, using an optical diffraction scattering particle sizedistribution meter (for example, trade name: N5 by Beckman Coulter, Inc.or trade name: Zetasizer 3000HSA by Malvern Instruments, Inc.).

Of the constituent components of the polishing agent of this embodiment,the hydroxide of a tetravalent metal element is believed to have a majoreffect on the polishing properties. Thus, adjusting the content of thehydroxide of a tetravalent metal element can improve chemicalinteraction between the abrasive grains and the surface to be polished,and further increase the polishing rate. Therefore, the content of thehydroxide of a tetravalent metal element is preferably 0.01 mass % orgreater, more preferably 0.03 mass % or greater and even more preferably0.05 mass % or greater, based on the total mass of the polishing agent.Also, from the viewpoint of easily avoiding aggregation of the abrasivegrains while obtaining satisfactory chemical interaction with thesurface to be polished and effectively making use of the abrasive grainproperties, the content of the hydroxide of a tetravalent metal elementis preferably 8 mass % or less, more preferably 5 mass % or less, evenmore preferably 3 mass % or less, especially preferably 1 mass % orless, extremely more preferably 0.5 mass % or less and very preferably0.3 mass % or less, based on the total mass of the polishing agent.

From the viewpoint of further increasing the polishing rate forinsulating materials, the lower limit for the abrasive grain content ispreferably 0.005 mass % or greater, more preferably 0.01 mass % orgreater, even more preferably 0.02 mass % or greater, especiallypreferably 0.04 mass % or greater and extremely preferably 0.05 mass %or greater, based on the total mass of the polishing agent. From theviewpoint of increasing the storage stability of the polishing agent,the upper limit for the abrasive grain content is preferably 20 mass %or less, more preferably 15 mass % or less and even more preferably 10mass % or less, based on the total mass of the polishing agent. Fromthese viewpoints, the abrasive grain content is more preferably 0.005mass % or greater and 20 mass % or less based on the total mass of thepolishing agent.

The abrasive grain content is preferably even further reduced to allowfurther reduction in cost and polishing scratches. A low abrasive graincontent will tend to lower the polishing rate for insulating materialsand the like. On the other hand, the abrasive grains containing ahydroxide of a tetravalent metal element allow a prescribed polishingrate to be obtained even when used in small amounts, and therefore theabrasive grain content can be further reduced while maintaining balancebetween the polishing rate and the advantages of reducing the abrasivegrain content. From this viewpoint, the abrasive grain content ispreferably 5 mass % or less, more preferably 3 mass % or less, even morepreferably 1 mass % or less, especially preferably 0.5 mass % or lessand extremely preferably 0.3 mass % or less.

[Absorbance]

The abrasive grains preferably comprise a hydroxide of a tetravalentmetal element and also satisfy at least one of the following conditions(a) and (b). An “aqueous dispersion” having an abrasive grain contentadjusted to a prescribed content is a liquid containing a prescribedcontent of abrasive grains and water.

(a) The abrasive grains produce absorbance of 1.00 or greater for lightwith a wavelength of 400 nm in an aqueous dispersion having the abrasivegrain content adjusted to 1.0 mass %.

(b) The abrasive grains produce absorbance of 1.000 or greater for lightwith a wavelength of 290 nm in an aqueous dispersion having the abrasivegrain content adjusted to 0.0065 mass %.

With regard to the condition (a), the polishing rate can be even furtherincreased by using abrasive grains that produce absorbance of 1.00 orgreater for light with a wavelength of 400 nm in an aqueous dispersionhaving the abrasive grain content adjusted to 1.0 mass %. The reason forthis is not fully understood, but the present inventors conjecture asfollows. Specifically, it is thought that particles, containingM(OH)_(a)X_(b) composed of a tetravalent metal (M⁴⁺), 1 to 3 hydroxideions (OH⁻) and 1 to 3 anions (X^(c-)) (wherein a+b×c=4), are produced aspart of the abrasive grains, depending on the production conditions forthe hydroxide of a tetravalent metal element (such particles are also“abrasive grains containing a hydroxide of a tetravalent metalelement”). In the formula M(OH)_(a)X_(b), presumably, theelectron-withdrawing anion (X^(c-)) acts to increase the hydroxide ionreactivity, thus the polishing rate increases as the abundance ofM(OH)_(a)X_(b) increases. Also, since the particles containingM(OH)_(a)X_(b) absorb light with a wavelength of 400 nm, presumably anincreased abundance of M(OH)_(a)X_(b) causes increased absorbance forlight with a wavelength of 400 nm, and increases the polishing rate.

Abrasive grains containing a hydroxide of a tetravalent metal elementpresumably contain not only M(OH)_(a)X_(b) but also M(OH)₄, MO₂ and thelike. The anion (X^(c-)) may be NO₃ ⁻ and SO₄ ²⁻, for example.

It is possible to confirm that the abrasive grain containing a hydroxideof a tetravalent metal element includes M(OH)_(a)X_(b) by the method ofdetecting the peak corresponding to the anion (X^(c-)) with FT-IR ATRmethod (Fourier transform Infra Red Spectrometer Attenuated TotalReflection method) after thoroughly washing the abrasive grain withpurified water. The presence of the anion (X^(c-)) can be also confirmedby XPS method (X-ray Photoelectron Spectroscopy method).

The absorption peak of M(OH)_(a)X_(b) (for example, M(OH)₃X) at awavelength of 400 nm has been confirmed to be much lower than theabsorption peak at a wavelength of 290 nm described below. In thisregard, as a result of studying degrees of absorbance using aqueousdispersions with relatively high abrasive grain contents of 1.0 mass %,which allow absorbance to be easily detected as high absorbance, thepresent inventors have found that the effect of increasing polishingrate is superior when using abrasive grains that produce absorbance of1.00 or greater for light with a wavelength of 400 nm in the aqueousdispersion. Incidentally, since it is thought that the absorbance forlight with a wavelength of 400 nm derives from the abrasive grains, asexplained above, it is difficult to obtain the effect of increasedpolishing rate with a polishing agent containing a substance (such as apigment component exhibiting a yellow color) that produces absorbance of1.00 or greater for light with a wavelength of 400 nm, instead ofabrasive grains that produce absorbance of 1.00 or greater for lightwith a wavelength of 400 nm.

With regard to the condition (b), the polishing rate can be even furtherincreased by using abrasive grains that produce absorbance of 1.000 orgreater for light with a wavelength of 290 nm in an aqueous dispersionhaving the abrasive grain content adjusted to 0.0065 mass %. The reasonfor this is not fully understood, but the present inventors conjectureas follows. Specifically, particles containing M(OH)_(a)X_(b) (forexample, M(OH)₃X) that are produced depending on the productionconditions for the hydroxide of a tetravalent metal element have acalculated absorption peak near a wavelength of 290 nm, and for example,particles composed of Ce⁴⁺(OH⁻)₃NO₃ ⁻ have an absorption peak at awavelength of 290 nm. Consequently, it is believed that the polishingrate is increased in accordance with the increase in absorbance forlight with a wavelength of 290 nm due to the increase in the abundanceof M(OH)_(a)X_(b).

The absorbance for light near a wavelength of 290 nm tends to bedetected to a greater degree as the measuring limit is exceeded. In thisregard, as a result of studying degrees of absorbance using aqueousdispersions with relatively low abrasive grain contents of 0.0065 mass%, which allow absorbance to be easily detected as low absorbance, thepresent inventors have found that the effect of increasing polishingrate is superior when using abrasive grains that produce absorbance of1.000 or greater for light with a wavelength of 290 nm in the aqueousdispersion. The present inventors have also found that, apart from lightnear a wavelength of 400 nm, which when absorbed by an absorbingsubstance tends to cause the absorbing substance to exhibit a yellowcolor, higher absorbance for light near a wavelength of 290 nm ofabrasive grains produces deeper yellowishness in a polishing agent andslurry employing such abrasive grains, and that deeper yellowishness ofthe polishing agent and slurry produces an increased polishing rate.Also, the present inventors found that the absorbance for light with awavelength of 290 nm in an aqueous dispersion with an abrasive graincontent of 0.0065 mass % and the absorbance for light with a wavelengthof 400 nm in an aqueous dispersion with an abrasive grain content of 1.0mass % are correlated.

The lower limit for the absorbance of light with a wavelength of 290 nmis preferably 1.000 or greater, more preferably 1.050 or greater, evenmore preferably 1.100 or greater, especially preferably 1.130 or greaterand extremely preferably 1.150 or greater, from the viewpoint ofallowing polishing of insulating materials at an even more superiorpolishing rate. The upper limit for the absorbance for light with awavelength of 290 nm is not particularly restricted, but is preferably10.00, for example.

If abrasive grains, producing absorbance of 1.00 or greater for lightwith a wavelength of 400 nm, produce absorbance of 1.000 or greater forlight with a wavelength of 290 nm in an aqueous dispersion having theabrasive grain content adjusted to 0.0065 mass %, it is possible topolish the insulating materials at an even more excellent polishingrate.

Also, hydroxides of the tetravalent metal element (such asM(OH)_(a)X_(b)) tend not to exhibit absorption for light withwavelengths of 450 nm or greater, and especially for light withwavelengths of 450 to 600 nm. Therefore, from the viewpoint ofminimizing adverse effects on polishing by the presence of impuritiesand accomplishing polishing of insulating materials at even moreexcellent polishing rates, the abrasive grains preferably produceabsorbance of 0.010 or less for light with a wavelength of 450 to 600 nmin an aqueous dispersion having the abrasive grain content adjusted to0.0065 mass % (65 ppm). Specifically, the absorbance preferably does notexceed 0.010 for all light within a wavelength range of 450 to 600 nm inan aqueous dispersion having the abrasive grain content adjusted to0.0065 mass %. The upper limit for the absorbance for light with awavelength of 450 to 600 nm is more preferably 0.005 or less and evenmore preferably 0.001 or less. The lower limit for the absorbance forlight with a wavelength of 450 to 600 nm is preferably 0.

The absorbance in an aqueous dispersion can be measured, for example,using a spectrophotometer (apparatus name: U3310) by Hitachi, Ltd.Specifically, an aqueous dispersion having the abrasive grain contentadjusted to 1.0 mass % or 0.0065 mass % is prepared as a measuringsample. Approximately 4 mL of the measuring sample is placed in a 1cm-square cell, and the cell is set in the apparatus. Spectrophotometryis then conducted in a wavelength range of 200 to 600 nm, and theabsorbance is judged from the obtained chart.

Screening of the absorbance may be accomplished by assuming that ifabsorbance of 1.00 or greater is exhibited when the absorbance for lightwith a wavelength of 400 nm is measured with excessive dilution so thatthe abrasive grain content is lower than 1.0 mass %, the absorbance willalso be 1.00 or greater when the abrasive grain content is 1.0 mass %.Screening of the absorbance may be accomplished by assuming that ifabsorbance of 1.000 or greater is exhibited when the absorbance forlight with a wavelength of 290 nm is measured with excessive dilution sothat the abrasive grain content is lower than 0.0065 mass %, theabsorbance will also be 1.000 or greater when the abrasive grain contentis 0.0065 mass %. Screening of the absorbance may be accomplished byassuming that if absorbance of 0.010 or less is exhibited when theabsorbance for light with a wavelength of 450 to 600 nm is measured withdilution so that the abrasive grain content is greater than 0.0065 mass%, the absorbance will also be 0.010 or less when the abrasive graincontent is 0.0065 mass %.

[Light Transmittance]

The polishing agent of this embodiment preferably has high transparencyfor visible light (it is visually transparent or nearly transparent).Specifically, the abrasive grains comprised in the polishing agent ofthis embodiment preferably produce light transmittance of 50%/cm orgreater for light with a wavelength of 500 nm in an aqueous dispersionhaving the abrasive grain content adjusted to 1.0 mass %. This canfurther inhibit reduction in polishing rate due to addition ofadditives, thus making it easier to obtain other properties whilemaintaining polishing rate. From this viewpoint, the lower limit for thelight transmittance is more preferably 60%/cm or greater, even morepreferably 70%/cm or greater, especially preferably 80%/cm or greater,extremely preferably 90%/cm or greater and very preferably 92%/cm orgreater. The upper limit for the light transmittance is 100%/cm.

Although the reason for which reduction in polishing rate can beinhibited by adjusting the light transmittance of the abrasive grains isnot thoroughly understood, the present inventors conjecture as follows.With abrasive grains containing a hydroxide of a tetravalent metalelement (such as cerium), chemical effects are believed to bepredominant over mechanical effects. Therefore, the number of abrasivegrains is believed to contribute to the polishing rate more than thesizes of the abrasive grains.

In the case of low light transmittance in an aqueous dispersion havingan abrasive grain content of 1.0 mass %, the abrasive grains present inthe aqueous dispersion presumably have relatively more particles withlarge particle diameters (hereunder referred to as “coarse particles”).When an additive (such as polyvinyl alcohol (PVA)) is added to apolishing agent containing such abrasive grains, other particlesaggregate around the coarse particles as nuclei, as shown in FIG. 1. Asa result, the number of abrasive grains acting on the surface to bepolished per unit area (the effective abrasive grain number) is reduced,thus the specific surface area of the abrasive grains contacting withthe surface to be polished is reduced, whereby presumably reduction inpolishing rate occurs.

Conversely, in the case of high light transmittance in an aqueousdispersion having an abrasive grain content of 1.0 mass %, the abrasivegrains present in the aqueous dispersion presumably have fewer “coarseparticles”. In such cases with a low abundance of coarse particles, asshown in FIG. 2, few coarse particles are available as nuclei foraggregation, and therefore aggregation between abrasive grains isinhibited or the sizes of the aggregated particles are smaller than theaggregated particles shown in FIG. 1, even when an additive (such aspolyvinyl alcohol) is added to the polishing agent. As a result, thenumber of abrasive grains acting on the surface to be polished per unitarea (the effective abrasive grain number) is maintained, thus thespecific surface area of the abrasive grains contacting with the surfaceto be polished is maintained, whereby presumably reduction in thepolishing rate hardly occur.

According to research by the present inventors, it was found that evenamong polishing agents having identical particle diameters to each otheras measured with a common particle diameter measuring apparatus, somemay be visually transparent (high light transmittance) and some may bevisually turbid (low light transmittance). This suggests that coarseparticles, which can produce the effect described above, can contributeto reduction in the polishing rate even in slight amounts that cannot bedetected with common particle diameter measuring apparatuses.

It has also been found that even repeated filtration to reduce theamount of coarse particles does not significantly improve the phenomenonof reduced polishing rate with addition of additives, and in some casesthe effect of increased polishing rate due to absorbance is notadequately exhibited. The present inventors found that this problem canbe overcome by using abrasive grains with high light transmittance inaqueous dispersion, for example, by modifying the method for producingthe abrasive grains.

The light transmittance is the transmittance for light with a wavelengthof 500 nm. The light transmittance can be measured using aspectrophotometer. Specifically, it can be measured with an U3310Spectrophotometer (apparatus name) by Hitachi, Ltd., for example.

As a more specific measuring method, an aqueous dispersion having theabrasive grain content adjusted to 1.0 mass % is prepared as a measuringsample. Approximately 4 mL of this measuring sample is placed in a 1cm-square cell, the cell is set in the apparatus, and then measurementis conducted. It is clear that, if the light transmittance is 50%/cm orgreater in an aqueous dispersion having an abrasive grain content ofgreater than 1.0 mass %, the light transmittance will also be 50%/cm orgreater when it is diluted to 1.0 mass %. Therefore, using an aqueousdispersion having an abrasive grain content of greater than 1.0 mass %allows screening of the light transmittance by a simple method.

The absorbance and light transmittance produced in the aqueousdispersion by abrasive grains comprised in the polishing agent can bemeasured by preparing an aqueous dispersion having a prescribed abrasivegrain content after removing the solid components other than theabrasive grains and the liquid components other than water, and usingthe aqueous dispersion for measurement. Depending on the components inthe polishing agent, the solid components and liquid components can beremoved, for example, using a centrifugal separation method such ascentrifugal separation using a centrifuge capable of applyinggravitational acceleration of up to several thousand G orultracentrifugation using an ultracentrifuge capable of applyinggravitational acceleration of several tens of thousands G or more; achromatographic method such as partition chromatography, adsorptionchromatography, gel permeation chromatography or ion-exchangechromatography; a filtration method such as natural filtration,filtration under reduced pressure, pressure filtration orultrafiltration; a distillation method such as vacuum distillation oratmospheric distillation, or a combination of the foregoing.

For example, when it contains a compound with a weight-average molecularweight of several tens of thousands or greater (for example, 50000 orgreater), a chromatographic method, filtration method or the like isexemplified, with gel permeation chromatography and ultrafiltrationbeing preferred among them. When a filtration method is to be used, theabrasive grains comprised in the polishing agent can pass through thefilter by appropriately setting the conditions. For example, when itcontains a compound with a weight-average molecular weight of up toseveral tens of thousands (for example, less than 50000), achromatographic method, filtration method, distillation method or thelike is exemplified, with gel permeation chromatography, ultrafiltrationand vacuum distillation being preferred among them. When a plural typesof abrasive grains are contained, a filtration method, centrifugalseparation method or the like is exemplified and more abrasive grainscontaining the hydroxide of a tetravalent metal element will be presentin the filtrate in the case of filtration or in the liquid phase in thecase of centrifugal separation.

With regard to the method of separating abrasive grains by achromatographic method, for example, the abrasive grain component can beseparated and/or the other components can be separated, under thefollowing conditions.

Sample Solution: Polishing Agent 100 μL

Detector: UV-VIS Detector by Hitachi, Ltd., trade name: “L-4200”,wavelength: 400 nm

Integrator: GPC integrator by Hitachi, Ltd., trade name: “D-2500”

Pump: Trade name: “L-7100” by Hitachi, Ltd.

Column: Aqueous HPLC packed column, trade name: “GL-W550S” by HitachiChemical Co., Ltd.

Eluent: Deionized water

Measuring temperature: 23° C.

Flow rate: 1 mL/min (pressure: approximately 40-50 kg/cm²)

Measuring time: 60 minutes

Before chromatography, eluent deaerating treatment is preferably carriedout using a deaeration apparatus. When a deaeration apparatus cannot beused, the eluent is preferably subjected to deaerating treatmentbeforehand with ultrasonic waves or the like.

Depending on the components comprised in the polishing agent, it may notbe possible to separate the abrasive grain component under theconditions described above, and in such cases, separation can beaccomplished by optimizing the sample solution amount, the column type,the eluent type, the measuring temperature, the flow rate and the like.Also, by adjusting the pH of the polishing agent to adjust the elutiontime of the components comprised in the polishing agent, it may bepossible to separate the abrasive grains. When the polishing agentcontains insoluble components, the insoluble components are preferablyremoved as necessary by filtration, centrifugal separation or the like.

[Method for Producing Abrasive Grains]

The hydroxide of a tetravalent metal element can be produced by reactinga tetravalent metal element salt (metal salt) with an alkaline source(base). The hydroxide of a tetravalent metal element is preferablyproduced by mixing a tetravalent metal element salt with an alkalisolution (for example, an aqueous alkali solution). This will allowparticles with extremely fine particle diameters to be obtained, so thatthe polishing agent with an even more excellent effect of reducingpolishing scratches can be obtained. This method is disclosed in PatentLiterature 5, for example. The hydroxide of a tetravalent metal elementcan be obtained by mixing a metal salt solution of a tetravalent metalelement salt (for example, an aqueous metal salt solution) with analkali solution. When either or both the tetravalent metal element saltand alkaline source is to be supplied to the reaction system in a liquidstate, there is no limitation to the means for mixing the liquidmixture. For example, there may be mentioned a method of stirring theliquid mixture using a rod, plate or propeller-shaped stirrer or astirring blade rotating around a rotating shaft, a method of stirringthe liquid mixture by rotating a stirrer in a rotating magnetic fieldusing a magnetic stirrer that transmits mechanical power from outside ofthe container, a method of stirring the liquid mixture with a pumpinstalled outside of the tank, and a method of stirring the liquidmixture by blowing in pressurized external air with force into the tank.The tetravalent metal element salt used may be a known one without anyparticular restrictions, and this includes M(NO₃)₄, M(SO₄)₂,M(NH₄)₂(NO₃)₆, M(NH₄)₄(SO₄)₄ (where M represents a rare earth metalelement), Zr(SO₄)₂.4H₂O and the like. M is preferably chemically activecerium (Ce).

The means for adjusting the absorbance or light transmittance may beoptimization of the method for producing the hydroxide of a tetravalentmetal element. The method of varying the absorbance for light with awavelength of 400 nm or the absorbance for light with a wavelength of290 nm may be, specifically, selecting the alkaline source in the alkalisolution, adjusting the raw material concentration of the metal saltsolution and the alkali solution, adjusting the mixing rate of the metalsalt solution and the alkali solution, or adjusting the liquidtemperature of the liquid mixture obtained by mixing the tetravalentmetal element salt and alkaline source. Also, the method of varying thelight transmittance for light with a wavelength of 500 nm may be,specifically, adjusting the raw material concentration of the metal saltsolution and the alkali solution, adjusting the mixing rate of the metalsalt solution and the alkali solution, adjusting the stirring speed formixing, or adjusting the liquid temperature of the liquid mixture.

In order to increase the absorbance for light with a wavelength of 400nm, the absorbance for light with a wavelength of 290 nm and lighttransmittance for light with a wavelength of 500 nm, the method forproducing the hydroxide of a tetravalent metal element is preferablymore “moderate”. Here, “moderate” means a moderate (slow) pH increasewhen the pH of the reaction system increases as the reaction proceeds.Conversely, in order to decrease the absorbance for light with awavelength of 400 nm, the absorbance for light with a wavelength of 290nm and light transmittance for light with a wavelength of 500 nm, themethod for producing the hydroxide of a tetravalent metal element ispreferably more “intense”. Here, “intense” means an intense (rapid) pHincrease when the pH of the reaction system increases as the reactionproceeds. In order to adjust the absorbance and light transmittancevalues to the prescribed ranges, it is preferred to optimize the methodfor producing the hydroxide of a tetravalent metal element based onthese tendencies. A method of controlling the absorbance and lighttransmittance will now be explained in greater detail.

{Alkaline Source}

A known alkaline source may be used in the alkali solution, without anyparticular restrictions. The alkaline source may be an organic base,inorganic base and the like. The organic base may be anitrogen-containing organic base such as guanidine, triethylamine andchitosan; a nitrogen-containing heterocyclic organic base such aspyridine, piperidine, pyrrolidine and imidazole; an ammonium salt suchas ammonium carbonate, ammonium hydrogencarbonate, tetramethylammoniumhydroxide (TMAH), tetraethylammonium hydroxide, tetramethylammoniumchloride and tetraethylammonium chloride. Inorganic bases may be ammoniaand inorganic salts of alkali metals such as lithium hydroxide, sodiumhydroxide, potassium hydroxide, calcium hydroxide, lithium carbonate,sodium carbonate, potassium carbonate, lithium hydrogencarbonate, sodiumhydrogencarbonate and potassium hydrogencarbonate. The alkaline sourceused may be a single type alone or a combination of two or more types.

From the viewpoint of further increasing the polishing rate forinsulating materials, the alkaline source is preferably ammonia andimidazole, and even more preferably imidazole. In order to increase theabsorbance for light with a wavelength of 400 nm and the absorbance forlight with a wavelength of 290 nm, the alkaline source used ispreferably an alkaline source exhibiting weak basicity. Among alkalinesources, nitrogen-containing heterocyclic organic bases are preferred,pyridine, piperidine, pyrrolidine and imidazole are more preferred,pyridine and imidazole are even more preferred, and imidazole isespecially preferred.

{Concentration}

The absorbance for light with a wavelength of 400 nm, the absorbance forlight with a wavelength of 290 nm and the light transmittance for lightwith a wavelength of 500 nm can be varied by controlling the rawmaterial concentrations in the metal salt solution and alkali solution.Specifically, the absorbance will tend to be increased with a highermetal salt concentration of the metal salt solution, while theabsorbance will tend to be increased with a lower alkaline concentration(base concentration, alkaline source concentration) of the alkalisolution. Also, the light transmittance will tend to be increased with ahigher metal salt concentration, while the light transmittance will tendto be increased with a lower alkaline concentration.

From the viewpoint of easily obtaining both excellent polishing rate andexcellent stability of the abrasive grains, the upper limit for themetal salt concentration of the metal salt solution is preferably 1.000mol/L or less, more preferably 0.500 mol/L or less, even more preferably0.300 mol/L or less and especially preferably 0.200 mol/L or less, basedon the total metal salt solution. The lower limit for the metal saltconcentration is preferably 0.010 mol/L or greater, more preferably0.020 mol/L or greater and even more preferably 0.030 mol/L or greater,based on the total metal salt solution, from the viewpoint of inhibitingrapid reaction (allowing the pH increase to be more moderate) whileincreasing the absorbance for light with a wavelength of 400 nm,absorbance for light with a wavelength of 290 nm and light transmittancefor light with a wavelength of 500 nm.

From the viewpoint of inhibiting rapid reaction, the upper limit for thealkaline concentration of the alkali solution is preferably 15.0 mol/Lor less, more preferably 12.0 mol/L or less and even more preferably10.0 mol/L or less, based on the total alkali solution. There is noparticular limit on the lower limit for the alkaline concentration, butfrom the viewpoint of productivity, it is preferably 0.001 mol/L orgreater based on the total alkali solution.

The alkaline concentration of the alkali solution is preferably adjustedas appropriate depending on the type of alkaline source selected. Forexample, with an alkaline source wherein the pKa of the conjugate acidof the alkaline source is 20 or higher, the upper limit for the alkalineconcentration is preferably 0.10 mol/L or less and more preferably 0.05mol/L or less, based on the total alkali solution, from the viewpoint ofinhibiting rapid reaction. There are no particular restrictions on thelower limit for the alkaline concentration, but from the viewpoint ofminimizing the amount of solution to be used for obtaining a prescribedamount of a hydroxide of a tetravalent metal element, it is preferably0.001 mol/L or greater based on the total alkali solution.

With an alkaline source wherein the pKa of the conjugate acid of thealkaline source is 12 or higher and lower than 20, the upper limit forthe alkaline concentration is preferably 1.0 mol/L or less and morepreferably 0.50 mol/L or less, based on the total alkali solution, fromthe viewpoint of inhibiting rapid reaction. There are no particularrestrictions on the lower limit for the alkaline concentration, but fromthe viewpoint of minimizing the amount of solution to be used forobtaining a prescribed amount of a hydroxide of a tetravalent metalelement, it is preferably 0.01 mol/L or greater based on the totalalkali solution.

With an alkaline source wherein the pKa of the conjugate acid of thealkaline source is lower than 12, the upper limit for the alkalineconcentration is preferably 15.0 mol/L or less and more preferably 10.0mol/L or less, based on the total alkali solution, from the viewpoint ofinhibiting rapid reaction. There are no particular restrictions on thelower limit for the alkaline concentration, but from the viewpoint ofminimizing the amount of solution to be used for obtaining a prescribedamount of a hydroxide of a tetravalent metal element, it is preferably0.10 mol/L or greater based on the total alkali solution.

An example of an alkaline source wherein the pKa of the conjugate acidof the alkaline source is 20 or greater includes1,8-diazabicyclo[5.4.0]undeca-7-ene (pKa: 25). Examples of alkalinesources wherein the pKa of the conjugate acid of the alkaline source is12 or higher and lower than 20 include potassium hydroxide (pKa: 16) andsodium hydroxide (pKa: 13). Examples of alkaline sources wherein the pKaof the conjugate acid of the alkaline source is lower than 12 includeammonia (pKa: 9) and imidazole (pKa: 7). The pKa value of the conjugateacid of the alkaline source to be used is not particularly restricted solong as the alkaline concentration is appropriately adjusted, but thepKa of the conjugate acid of the alkaline source is preferably lowerthan 20, more preferably lower than 12, even more preferably lower than10 and especially preferably lower than 8.

{Mixing Rate}

The absorbance for light with a wavelength of 400 nm, the absorbance forlight with a wavelength of 290 nm and the light transmittance for lightwith a wavelength of 500 nm can be varied by controlling the mixing rateof the metal salt solution and alkali solution. The absorbance and lighttransmittance respectively tend to be increased when the pH increase ismoderate (slow). More specifically, the absorbance tends to be higherwhen the mixing rate is decreased, while the absorbance tends to belower when the mixing rate is increased. Also, the light transmittancetends to be higher when the mixing rate is decreased, while the lighttransmittance tends to be lower when the mixing rate is increased.

The upper limit for the mixing rate is preferably 5.00×10⁻³ m³/min (5L/min) or less, more preferably 1.00×10⁻³ m³/min (1 L/min) or less, evenmore preferably 5.00×10⁻⁴ m³/min (500 mL/min) or less and especiallypreferably 1.00×10⁻⁴ m³/min (100 mL/min) or less, from the viewpoint offurther inhibiting rapid reaction while further inhibiting localimbalance of the reaction. The lower limit for the mixing rate is notparticularly restricted, but is preferably 1.00×10⁻⁷ m³/min (0.1 mL/min)or greater from the viewpoint of productivity.

{Stirring Speed}

By controlling the stirring speed for mixing of the metal salt solutionand the alkali solution, it is possible to vary the light transmittancefor light with a wavelength of 500 nm. Specifically, the lighttransmittance tends to be higher when the stirring speed is increased,while the light transmittance tends to be lower when the stirring speedis decreased.

From the viewpoint of further inhibiting local imbalance of the reactionand obtaining excellent mixing efficiency, the lower limit for thestirring speed is preferably 30 min⁻¹ or greater, more preferably 50min⁻¹ or greater and even more preferably 80 min⁻¹ or greater. The upperlimit for the stirring speed is not particularly restricted, and it willneed to be appropriately adjusted depending on the size and shape of thestirring blade, but it is preferably 1000 min⁻¹ or less from theviewpoint of preventing splashing of liquid.

{Liquid Temperature (Synthesis Temperature)}

By controlling the liquid temperature of the liquid mixture obtained bymixing the tetravalent metal element salt and the alkaline source, it ispossible to vary the absorbance for light with a wavelength of 400 nm,the absorbance for light with a wavelength of 290 nm and the lighttransmittance for light with a wavelength of 500 nm, and to obtainabrasive grains that allow the desired polishing rate and storagestability to be achieved. Specifically, the absorbance tends to behigher when the liquid temperature is reduced, while the absorbancetends to be lower when the liquid temperature is increased. Also, thelight transmittance tends to be higher when the liquid temperature isreduced, while the light transmittance tends to be lower when the liquidtemperature is increased.

The liquid temperature is, for example, the temperature in the liquidmixture as read from a thermometer set in the liquid mixture, and it ispreferably 0° C. to 100° C. The upper limit for the liquid temperatureis preferably 100° C. or less, more preferably 60° C. or less, even morepreferably 55° C. or less, especially preferably 50° C. or less andextremely preferably 45° C. or less, from the viewpoint of allowingrapid reaction to be inhibited. From the viewpoint of facilitatingprogression of the reaction, the lower limit for the liquid temperatureis preferably 0° C. or greater, more preferably 10° C. or greater andeven more preferably 20° C. or greater.

The hydroxide of a tetravalent metal element synthesized by the methodabove sometimes contains impurities (for example, metal impurities), butthe impurities can be removed by washing. Washing of the hydroxide of atetravalent metal element may be accomplished by a method of repeatedsolid-liquid separation by centrifugal separation or the like. Washingcan also be accomplished by ion removal, using centrifugal separation,dialysis, ultrafiltration, an ion exchange resin, or the like. Theabsorbance for light with a wavelength of 450 to 600 nm can be adjustedby removing impurities.

When the obtained abrasive grains are aggregated, they can be dispersedin water by an appropriate method. The method for dispersing theabrasive grains in water as the major dispersing medium may bemechanical dispersion treatment with a homogenizer, ultrasonicdisperser, wet ball mill or the like, in addition to dispersiontreatment with a stirrer. The dispersion method and particle diametercontrol method may be the methods described in Non-Patent Literature 1,for example. Also, the washing treatment above may be carried out tolower the electric conductivity of the dispersion containing theabrasive grains (500 mS/m or less, for example), thereby increasing thedispersibility of the abrasive grains. Thus, the washing treatment abovemay be applied as dispersion treatment, or the washing treatment aboveand dispersion treatment may be combined.

(Additives)

The polishing agent of this embodiment comprises an additive. Here,“additive” refers to a substance that is added to the polishing agent inaddition to water and abrasive grains, in order to adjust the polishingproperties such as polishing rate and polishing selectivity; thepolishing agent properties such as abrasive grain dispersibility andstorage stability; and the like.

[First Additive: Glycerin Compound]

The polishing agent of this embodiment comprises a glycerin compound asthe first additive. The first additive has an effect of increasing thepolishing rate for the insulating material. Presumably, the hydroxylgroup of the glycerin compound interacts with the abrasive grains andinsulating material to bridge the abrasive grains and the insulatingmaterial with hydrogen bonding, and therefore, interaction between theabrasive grains and the insulating material can be increased. The firstadditive also has an effect of inhibiting the polishing rate for thestopper material. Presumably, the hydroxyl group of the glycerincompound interacts with the abrasive grains to increase thehydrophilicity of the abrasive grain surfaces, and therefore,interaction between the abrasive grains and the hydrophobic stoppermaterial can be reduced. However, the action mechanism is not limited tothe one described above.

A first aspect of the glycerin compound is at least one selected fromthe group consisting of compounds represented by general formula (I)below and compounds represented by general formula (II) below.[Chemical Formula 5]HO

C₃H₅(OH)—O

_(m)H  (I)[In formula (I), m is an integer of 3 or greater.]

[In formula (II), n represents an integer of 2 or greater, and R¹, R²and the multiple R³ each independently represent hydrogen atom, a grouprepresented by general formula (III) below or a group represented bygeneral formula (IV) below. The case where R¹, R² and the multiple R³are all hydrogen atom is excluded.][Chemical Formula 7]

CH₂—CH₂.O

_(p)H  (III)[In formula (III), p represents an integer of 1 or greater.]

[In formula (IV), q represents an integer of 1 or greater.]

In formula (I), m is 3 or greater, preferably 4 or greater, morepreferably 5 or greater and even more preferably 10 or greater, from theviewpoint of increasing the polishing rate for the insulating material.From the viewpoint of production, m is preferably 100 or less, morepreferably 50 or less and even more preferably 30 or less.

In formula (I), the structural unit of the [C₃H₅(OH)O] portion may be,for example, a structural unit represented by any of formulas (Va) to(Vc) below. The compound represented by formula (I) may be a compoundhaving one type from among formulas (Va) to (Vc), or it may be acompound having more than one from among formulas (Va) to (Vc). In acompound having more than one from among formulas (Va) to (Vc), thearrangement of the structural units may be as desired. For example, itmay have any desired form such as (a) the form of a block copolymer withthe same structural units in continuity, (b) the form of a randomcopolymer having a structural unit A and a structural unit B arranged inno particular order, or (c) the form of an alternating copolymer havinga structural unit A and a structural unit B in an alternatingarrangement. An example of compounds represented by formula (I) includescompounds represented by formula (VIa) below and compounds representedby formula (VIb) below.

[In formula (VIa), r1 represents an integer of 0 or greater, s1represents an integer of 0 or greater, and r1+s1 is an integer of 3 orgreater.]

[In formula (VIb), r2 represents an integer of 0 or greater, s2represents an integer of 0 or greater, and r2+s2 is an integer of 3 orgreater.]

The compound represented by formula (VIa) may lack one of the[CH₂CH(OH)CH₂O] portion and [CH₂CH(CH₂OH)O] portion (i.e. r1=0 or s1=0may be satisfied). The compound represented by formula (VIb) may lackone of the [CH₂CH(OH)CH₂O] portion and [CH(CH₂OH)CH₂O] portion (i.e.r2=0 or s2=0 may be satisfied). The arrangement of the structural unitin the curly brackets in formula (VIa) and formula (VIb) (that is, the[CH₂CH(OH)CH₂O] portion and [CH₂CH(CH₂OH)O] portion in formula (VIa),and the [CH₂CH(OH)CH₂O] portion and [CH(CH₂OH)CH₂O] portion in formula(VIb)) may be as desired.

From the viewpoint of increasing the polishing rate for insulatingmaterials, n is 2 or greater. From the viewpoint of production, n ispreferably 100 or less, more preferably 50 or less and even morepreferably 30 or less.

From the viewpoint of further increasing the polishing rate forinsulating materials, p in formula (III) is preferably 2 or greater andmore preferably 5 or greater. From the viewpoint of further increasingthe polishing rate for insulating materials, p is preferably 200 orless, more preferably 150 or less, even more preferably 100 or less andespecially preferably 50 or less. From the viewpoint of furtherincreasing the polishing rate for insulating materials, q in formula(IV) is preferably 2 or greater and more preferably 5 or greater. Fromthe viewpoint of further increasing the polishing rate for insulatingmaterials, q is preferably 200 or less, more preferably 150 or less,even more preferably 100 or less and especially preferably 50 or less.

A second aspect of the glycerin compound is the aspect wherein theglycerin compound is at least one selected from the group consisting ofpolyglycerin, diglycerin derivatives and polyglycerin derivatives, andthe HLB value of the glycerin compound is 19.8 to 20.0. The secondaspect of the glycerin compound may be the compound which is the firstaspect of the glycerin compound.

Polyglycerin is a polyglycerin with a glycerin mean polymerizationdegree of 3 or greater (polyglycerin that is a trimer or more). Thelower limit for the mean polymerization degree of the polyglycerin is 3or greater, preferably 4 or greater, more preferably 5 or greater andeven more preferably 10 or greater, from the viewpoint of increasing thepolishing rate for insulating materials. There are no particularrestrictions on the upper limit for the mean polymerization degree ofthe polyglycerin, but from the viewpoint of production, it is preferably100 or less, more preferably 50 or less and even more preferably 30 orless. From these viewpoints, the mean polymerization degree of thepolyglycerin is more preferably 3 or greater and 100 or less.

A diglycerin derivative is a compound having a functional groupintroduced into diglycerin. The functional group may be apolyoxyalkylene group or the like. The diglycerin derivative may be apolyoxyalkylene diglyceryl ether or the like. Polyoxyalkylene diglycerylether may be polyoxyethylene diglyceryl ether (for example, SC-E Seriesby Sakamoto Yakuhin Kogyo Co., Ltd.) and polyoxypropylene diglycerylether (for example, SY-DP Series by Sakamoto Yakuhin Kogyo Co., Ltd.) orthe like.

A polyglycerin derivative is a compound having a functional groupintroduced into polyglycerin having a mean glycerin polymerizationdegree of 3 or greater. The functional group may be polyoxyalkylenegroup or the like. The polyglycerin derivative may be polyoxyalkylenepolyglyceryl ether or the like. The polyoxyalkylene polyglyceryl ethermay be polyoxyethylene polyglyceryl ether, polyoxypropylene polyglycerylether or the like.

The ULB value for the second aspect of the glycerin compound is 19.8 orgreater and preferably 19.9 or greater, from the viewpoint of excellentdispersion stability. The HLB value for the second aspect of theglycerin compound is 20.0 or less, from the viewpoint of excellentpolishing selectivity for insulating materials with respect to stoppermaterials. The ULB value for the second aspect of the glycerin compoundis more preferably 20.0, from the viewpoint of more excellent polishingselectivity for insulating materials with respect to stopper materials.

The “HLB value” is a value representing the hydrophilic/lipophilicbalance of a compound. The HLB value can be determined by calculationeven when the type of hydrophobic group, the type of hydrophilic group,the copolymerization ratio or the like are different in a singlecompound.

Several methods have been proposed for calculating the HLB value. Forexample, the HLB value is calculated by the Griffin method, representedby the following formula.HLB value=20×(total molecular weight of hydrophilic portion)/(entiremolecular weight)

An example of hydrophilic group includes hydroxyl group, glyceryl group,oxyethylene group, oxypropylene group, hydroxypropyl group, carboxylgroup and sulfonic acid group. For example, the compound represented byformula (II) has an R¹ group, an OR² group and an OC₃H₅OR³ group. R¹, R²and R³ are all hydrophilic groups, and the OR² group and OC₃H₅OR³ groupare hydrophilic group portions. Thus, the HLB value of a compoundrepresented by formula (II) is calculated to be about 20.0.

A glycerin compound may not be a single molecule, or it may have someextent of molecular weight distribution. The HLB value of a glycerincompound can be obtained using the average of measured values obtainedby measurement according to the following method.

The HLB value of a glycerin compound in a polishing agent can bedetermined by separation of the glycerin compound from the polishingagent using centrifugation, chromatography, filtration, distillation orthe like, followed by concentration or the like if necessary, andidentification of the structure of the compound using ¹³C-NMR, ¹H-NMR,GPC, MALDI-MS (Matrix Assisted Laser Desorption/Ionization-MassSpectrometry) or the like. For example, the proportion of structuralunits or the like can be determined from the ¹H-NMR spectrum. Also, theproportion of structural units and the terminal structure can beidentified from the MALDI-MS spectrum. In addition, the copolymerizationform of the structural units or the like can be analyzed from the¹³C-NMR spectrum.

The first additive used may be a single type or a combination of two ormore types, for the purpose of adjusting the polishing selectivity forinsulating materials with respect to stopper materials, the flatness,the insulating material polishing rate and the like. In addition, aplurality of compounds with different polymerization degrees may be usedin combination.

The upper limit for the weight-average molecular weight of the firstadditive is not particularly restricted, but from the viewpoint ofworkability and foamability, it is preferably 10×10³ or less, morepreferably 5.0×10³ or less, even more preferably 3.0×10³ or less andespecially preferably 2.0×10³ or less. When the first additive is apolyglycerin derivative or diglycerin derivative, the weight-averagemolecular weight of the first additive is more preferably 5.0×10³ orless, even more preferably 3.0×10³ or less and especially preferably2.0×10³ or less, from the viewpoint of avoiding reduced polishing ratedue to overly excessive molecular weight of the functional groups in thederivative. The lower limit for the weight-average molecular weight ofthe first additive is preferably 250 or greater, more preferably 400 orgreater and even more preferably 500 or greater, from the viewpoint offurther increasing the polishing rate for insulating materials. When thefirst additive is polyglycerin, it is preferably 250 or greater, morepreferably 400 or greater, even more preferably 500 or greater,especially preferably 750 or greater, very preferably 1.0×10³ or greaterand extremely preferably 1.2×10³ or greater, from the viewpoint offurther increasing the polishing rate for insulating materials. Fromthese viewpoints, the weight-average molecular weight of the firstadditive is more preferably 250 or greater and 10×10³ or less.

The weight-average molecular weight of the first additive can bemeasured by gel permeation chromatography (GPC) under the followingconditions, using a standard polystyrene calibration curve, for example.

Device: Hitachi Model L-6000 [product of Hitachi, Ltd.]

Column: GL-R420 Gel pack+GL-R430 Gel pack+GL-R440 Gel pack (total of 3,trade name of Hitachi Chemical Co., Ltd.)

Eluent: Tetrahydrofuran

Measuring temperature: 40° C.

Flow rate: 1.75 mL/min

Detector: L-3300RI [Hitachi, Ltd.]

From the viewpoint of further increasing the polishing rate forinsulating materials, the lower limit for the first additive content ispreferably 0.01 mass % or greater, more preferably 0.04 mass % orgreater, even more preferably 0.1 mass % or greater and especiallypreferably 0.3 mass % or greater, based on the total mass of thepolishing agent. From the viewpoint of inhibiting excessive increase inthe viscosity of the polishing agent, the upper limit for the firstadditive content is preferably 10 mass % or less and more preferably 5mass % or less, based on the total mass of the polishing agent. Fromthese viewpoints, the first additive content is more preferably 0.01mass % or greater and 10 mass % or less, based on the total mass of thepolishing agent. When a plurality of compounds is to be used as thefirst additive, the total content of each of the compounds preferablysatisfies the range specified above.

[Second Additive]

The polishing agent of this embodiment may further comprise a secondadditive, in addition to the first additive, in order to modify thepolishing properties such as polishing rate; the polishing agentproperties such as abrasive grain dispersibility and storage stability;and the like.

The second additive may be a carboxylic acid, amino acid or the like.The second additive may be used as a single type alone or as acombination of two or more types. Preferred among these for the secondadditive are carboxylic acids and amino acids, from the viewpoint ofexcellent balance between abrasive grain dispersibility and polishingproperties.

A carboxylic acid has an effect of stabilizing the pH while furtherincreasing the polishing rate for insulating materials. An example ofthe carboxylic acid includes formic acid, acetic acid, propionic acid,butyric acid, valeric acid, caproic acid and lactic acid.

An amino acid has an effect of improving the dispersibility of theabrasive grains containing the hydroxide of a tetravalent metal element,and further increasing the polishing rate for insulating materials. Anexample of the amino acid includes arginine, lysine, aspartic acid,glutamic acid, asparagine, glutamine, histidine, proline, tyrosine,tryptophan, serine, threonine, glycine, alanine, β-alanine, methionine,cysteine, phenylalanine, leucine, valine and isoleucine. An amino acidhas a carboxyl group, but it is defined as one different from acarboxylic acid.

When a second additive is used, the content of the second additive ispreferably 0.01 mass % or greater and 10 mass % or less, based on thetotal mass of the polishing agent, from the viewpoint of obtaining theeffects of adding the additives while minimizing sedimentation of theabrasive grains. When a plurality of compounds is to be used as thesecond additive, the total content of each of the compounds preferablysatisfies the range specified above.

(Water-Soluble Polymer)

The polishing agent of this embodiment may comprise a water-solublepolymer, for the purpose of adjusting the polishing properties such asflatness, in-plane uniformity, polishing selectivity for silicon oxidewith respect to silicon nitride (polishing rate for siliconoxide/polishing rate for silicon nitride), and polishing selectivity forsilicon oxide with respect to polysilicon (polishing rate for siliconoxide/polishing rate for polysilicon). A “water-soluble polymer” isdefined as a polymer dissolved to at least 0.1 g in 100 g of water. Thefirst additive is not included in the term “water-soluble polymer”.

There are no particular restrictions on the water-soluble polymer.Specific example of the water-soluble polymers includes polysaccharidessuch as alginic acid, pectic acid, carboxymethyl cellulose, agar,curdlan, dextrin, cyclodextrin, chitosan, chitosan derivatives andpullulan; vinyl-based polymers such as polyvinyl alcohol,polyvinylpyrrolidone and polyacrolein; acrylic polymers such aspolyacrylamide and polydimethylacrylamide; amine polymers such aspolyallylamine, polyethyleneimine and polydiallylamines; andpolyethylene glycol, polyoxypropylene, polyoxyethylene-polyoxypropylenecondensation products, ethylenediamine polyoxyethylene-polyoxypropyleneblock copolymers, and the like. These water-soluble polymers may also bederivatives. Of these water-soluble polymers, amine polymers and theirderivatives are preferred and polyallylamines and their derivatives aremore preferred, from the viewpoint of further improving polishingselectivity for insulating materials with respect to stopper materials.The water-soluble polymer may be used as a single type alone or as acombination of two or more types.

The weight-average molecular weight of the water-soluble polymer ispreferably 100 or greater, more preferably 300 or greater, even morepreferably 500 or greater and especially preferably 1.0×10³ or greater,from the viewpoint of further improving the polishing selectivity forinsulating materials with respect to stopper materials. Theweight-average molecular weight of the water-soluble polymer ispreferably 300×10³ or less, more preferably 100×10³ or less, even morepreferably 50×10³ or less and especially preferably 30×10³ or less, fromthe viewpoint of further improving the polishing selectivity forinsulating materials with respect to stopper materials. From theseviewpoints, the weight-average molecular weight of the water-solublepolymer is more preferably 100 or greater and 300×10³ or less. Theweight-average molecular weight of the water-soluble polymer can bemeasured by the same method as for the weight-average molecular weightof the first additive.

When a water-soluble polymer is used, the content of the water-solublepolymer is preferably 0.0001 mass % or greater, more preferably 0.00015mass % or greater and even more preferably 0.0002 mass % or greater,based on the total mass of the polishing agent, from the viewpoint ofobtaining the effect of adding the water-soluble polymer whileminimizing sedimentation of the abrasive grains. The content of thewater-soluble polymer is preferably 5 mass % or less, more preferably 3mass % or less and even more preferably 1 mass % or less, based on thetotal mass of the polishing agent, from the viewpoint of obtaining theeffect of adding the water-soluble polymer while minimizingsedimentation of the abrasive grains. From these viewpoints, the contentof the water-soluble polymer is more preferably 0.0001 mass % or greaterand 5 mass % or less. When a plurality of compounds is to be used as thewater-soluble polymer, the total content of each of the compoundspreferably satisfies the range specified above.

(Polishing Agent Properties)

The lower limit for the pH (25° C.) of the polishing agent of thisembodiment is preferably 3.0 or greater, more preferably 4.0 or greater,even more preferably 4.5 or greater and especially preferably 5.0 orgreater, from the viewpoint of further increasing the polishing rate forinsulating materials. Also, the upper limit for the pH is preferably12.0 or less, more preferably 11.0 or less, even more preferably 10.0 orless, especially preferably 9.0 or less and extremely preferably 8.0 orless, from the viewpoint of further increasing the polishing rate forinsulating materials. From these viewpoints, the pH of the polishingagent is more preferably 3.0 or greater and 12.0 or less.

The pH of the polishing agent can be adjusted with an acid componentsuch as an inorganic acid or organic acid; an alkaline component such asammonia, sodium hydroxide, tetramethylammonium hydroxide (TMAH) orimidazole; or the like. A buffering agent may also be added to stabilizethe pH. A buffering agent may also be added using a buffer solution (abuffering agent-containing solution). An example of such buffersolutions includes acetate buffer solutions and phthalate buffersolutions.

The pH of the polishing agent of this embodiment can be measured with apH meter (for example, a Model PHL-40 by DKK Corp.). Specifically, forexample, after 2-point calibration of a pH meter using phthalate pHbuffer solution (pH 4.01) and a neutral phosphate pH buffer solution (pH6.86) as standard buffer solutions, the pH meter electrode was placed inthe polishing agent, and then the value was measured after at least 2minutes passed for stabilization. Here, the liquid temperature of thestandard buffer solution and polishing agent are both 25° C.

The polishing agent of this embodiment may be stored as a one-packpolishing agent containing at least the abrasive grains, the firstadditive and water, or it may be stored as a multi-pack (for example,two-pack) polishing agent set comprising constituent components dividedinto a slurry (first liquid) and an additive solution (second liquid) sothat the slurry and additive solution are mixed to form the polishingagent. The slurry contains at least the abrasive grains and water, forexample. The additive solution contains the first additive and water,for example. Between the slurry and the additive solution, the firstadditive, second additive, water-soluble polymer and buffering agent arepreferably contained in the additive solution. The constituentcomponents of the polishing agent may be stored as a polishing agent setdivided into three or more liquids.

In such a polishing agent set, the slurry and the additive solution aremixed immediately before polishing or during polishing to prepare thepolishing agent. Also, a one-pack polishing agent may be stored as apolishing agent storage solution with a reduced water content, and usedby dilution with water at the time of polishing. A multi-pack polishingagent set may be stored as a slurry storage solution and additivesolution storage solution with reduced water contents, and used bydilution with water at the time of polishing.

In the case of a one-pack polishing agent, the method used to supply thepolishing agent onto the polishing platen may be a method of supplyingthe polishing agent by direct liquid conveyance; a method of separatelyconveying the polishing agent storage solution and water throughtubings, merging them together and then supplying; or a method of mixingthe polishing agent storage solution and water beforehand and thensupplying.

For storage as a multi-pack polishing agent set separately comprising aslurry and additive solution, the polishing rate can be adjusted byoptionally varying the composition of these liquids. When a polishingagent set is used for polishing, the following method may be used as themethod for supplying the polishing agent onto the polishing platen. Forexample, there may be employed a method of separately conveying theslurry and additive solution through tubings and merging the tubings tomix and then supplying; a method of separately conveying the slurrystorage solution, additive solution storage solution and water throughtubings and merging the tubings to mix and then supplying; a method ofmixing the slurry and additive solution beforehand and then supplying;or a method of mixing the slurry storage solution, additive solutionstorage solution and water beforehand and then supplying. There may alsobe employed a method in which the slurry and additive solution of thepolishing agent set are each supplied onto the polishing platen. In thiscase, the polishing agent obtained by mixing the slurry and additivesolution on the polishing platen are used for polishing of the surfaceto be polished.

(Polishing Method for Base Substrate)

The polishing method for a base substrate of this embodiment maycomprise a polishing step of polishing the surface to be polished of abase substrate using the one-pack polishing agent, or it may comprise apolishing step of polishing the surface to be polished of a basesubstrate using the polishing agent obtained by mixing the slurry andthe additive solution of the polishing agent set. Also, the polishingmethod for a base substrate of this embodiment may be a polishing methodfor a base substrate having an insulating material and polysilicon, andfor example, it may comprise a polishing step of selectively polishingthe insulating material with respect to the polysilicon using theone-pack polishing agent, or the polishing agent obtained by mixing theslurry and the additive solution of the polishing agent set. In thiscase, the base substrate may have a member comprising the insulatingmaterial and a member comprising the polysilicon, for example.“Selectively polish material A with respect to material B” means thatthe polishing rate for material A is higher than the polishing rate formaterial B under the same polishing conditions. More specifically, itmeans, for example, that material A is polished with the polishing rateratio of the polishing rate for material A with respect to the polishingrate for material B being 10 or greater.

In the polishing step, for example, under the condition that thematerial to be polished of the base substrate that has the material tobe polished is pressed against the abrasive pad (abrasive cloth) of apolishing platen, the polishing agent is supplied between the materialto be polished and the abrasive pad, and the base substrate andpolishing platen are moved relative to each other to polish the surfaceto be polished of the material to be polished. For example, at least aportion of the material to be polished is removed by the polishing inthe polishing step.

The base substrate that is to be polished may be a substrate or thelike, and for example, it may be a substrate comprising a material to bepolished formed on a substrate for semiconductor element production (forexample, a semiconductor substrate in which an STI pattern, gate patternor wiring pattern has been formed). An example of the material to bepolished includes an insulating material such as silicon oxide; astopper material such as polysilicon and silicon nitride. The materialto be polished may be a single material or a plurality of materials.When a plurality of materials is exposed on the surface to be polished,they may be considered as the material to be polished. The material tobe polished may be in the form of a film, such as a silicon oxide film,polysilicon film and silicon nitride film.

By polishing a material to be polished (for example, an insulatingmaterial such as silicon oxide) formed on such substrate with thepolishing agent and removing the unwanted sections, it is possible toeliminate irregularities on the surface of the material to be polishedand to produce a smooth surface over the entire surface of the materialto be polished. The polishing agent of this embodiment is preferablyused for polishing of a surface to be polished containing silicon oxide.

In this embodiment, it is possible to polish an insulating material of abase substrate having an insulating material containing silicon oxide onat least the surface, a stopper (polishing stop layer) disposed as thelower layer of the insulating material, and a semiconductor substratedisposed under the stopper. The stopper material composing the stopperis a material with a lower polishing rate than the insulating material,and it is preferably polysilicon, silicon nitride or the like. With sucha substrate, excessive polishing of the insulating material is preventedby stopping the polishing when the stopper have exposed, and this canimprove flatness of the insulating material after polishing.

An example of the forming method for a material to be polished by thepolishing agent of this embodiment includes a CVD method such aslow-pressure CVD method, normal-pressure CVD method and plasma CVDmethod; a spin coating method in which the liquid material is coatedonto the substrate that is spinning.

Silicon oxide is obtained using low-pressure CVD method, for example, bythermal reaction of monosilane (SiH₄) and oxygen (O₂). Silicon oxide isalso obtained using normal-pressure CVD method, for example, by thermalreaction of tetraethoxysilane (Si(OC₂H₅)₄) and ozone (O₃). As anotherexample, silicon oxide is likewise obtained by plasma reaction oftetraethoxysilane and oxygen.

Silicon oxide is obtained using a spin coating method, for example, bycoating a liquid starting material containing inorganic polysilazane,inorganic siloxane or the like onto a substrate and conductingthermosetting reaction in a furnace body or the like.

An example of the forming method for polysilicon includes low-pressureCVD method in which monosilane is subjected to thermal reaction, andplasma CVD method in which monosilane is subjected to plasma reaction.

Example of the forming method for silicon nitride includes low-pressureCVD method in which dichlorsilane and ammonia are thermally reacted, andplasma CVD method in which monosilane, ammonia and nitrogen aresubjected to plasma reaction. The silicon nitride obtained by such amethod may contain elements other than silicon and nitrogen, such ascarbon or hydrogen, in order to adjust the material quality.

In order to stabilize the materials such as silicon oxide, polysiliconand silicon nitride that are obtained by such methods, heat treatmentmay be carried out at a temperature of 200° C. to 1000° C. as necessary.The silicon oxide obtained by such methods may also contain smallamounts of boron (B), phosphorus (P), carbon (C) or the like in order toincrease the embedding property.

The polishing method of this embodiment will now be explained using apolishing method for a semiconductor substrate on which an insulatingmaterial has been formed, as an example. In the polishing method of thisembodiment, the polishing apparatus used may be a common polishingapparatus having a holder capable of holding the base substrate, such asa semiconductor substrate, that has the surface to be polished, and apolishing platen on which an abrasive pad can be mounted. Rotationalspeed-variable motors or the like may be mounted on the holder and thepolishing platen, respectively. An example of the polishing apparatusincludes the polishing apparatus: Reflexion by Applied Materials, Inc.

The abrasive pad used may be a common nonwoven fabric, foam body,non-foam body or the like. The abrasive pad material used may be a resinsuch as polyurethane, acryl, polyester, acryl-ester copolymer,polytetrafluoroethylene, polypropylene, polyethylene,poly-4-methylpentene, cellulose, cellulose ester, polyamide (forexample, nylon (trademark) and aramid), polyimide, polyimideamide,polysiloxane copolymer, oxirane compound, phenol resin, polystyrene,polycarbonate, epoxy resin and the like. Especially, the abrasive padmaterial is preferably polyurethane foam and non-foam polyurethane, fromthe viewpoint of polishing rate and flatness. The abrasive pad ispreferably furrowed to allow accumulation of the polishing agent.

There are no particular restrictions on the polishing conditions, butthe rotational speed of the polishing platen is preferably 200 min⁻¹ orless so that the semiconductor substrate does not fly out, the polishingpressure (machining load) on the semiconductor substrate is preferably100 kPa or less from the viewpoint of adequately inhibiting thegeneration of polishing scratches. The polishing agent is preferablycontinuously supplied to the abrasive pad with a pump or the like duringpolishing. The amount supplied is not particularly restricted, butpreferably the surface of the abrasive pad is covered by the polishingagent at all times.

The semiconductor substrate after polishing is preferably thoroughlycleaned in flowing water to remove the particles adhering to thesubstrate. The cleaning may be carried out using dilute hydrofluoricacid or ammonia water in addition to purified water, and a brush may beused together to increase the cleaning efficiency. Also, it is preferredthat, after cleaning, the water droplets adhering to the semiconductorsubstrate are removed off using a spin dryer or the like, and then thesemiconductor substrate is dried.

The polishing agent, polishing agent set and polishing method of thisembodiment can be suitably employed for formation of an STI. Forformation of an STI, the polishing rate ratio for the insulatingmaterial (for example, silicon oxide) with respect to the stoppermaterial (for example, polysilicon) is preferably 10 or greater and morepreferably 12 or greater. If the polishing rate ratio is lower than 10,the magnitude of the polishing rate for the insulating material withrespect to the polishing rate for the stopper material is small, andtherefore, it will tend to be difficult to halt polishing at theprescribed location during formation of the STI. If the polishing rateratio is 10 or greater, on the other hand, it will be easier to haltpolishing, which is more suitable for STI formation.

The polishing agent, polishing agent set and polishing method of thisembodiment can also be employed for polishing of pre-metal insulatingmaterials. Examples of pre-metal insulating materials include, inaddition to silicon oxide, also phosphorus-silicate glass andboron-phosphorus-silicate glass, as well as silicon oxyfluoride andfluorinated amorphous carbon.

The polishing agent, polishing agent set and polishing method of thisembodiment can also be employed for materials other than insulatingmaterials such as silicon oxide. An Example of such material includeshigh permittivity materials such as Hf-based, Ti-based and Ta-basedoxides; semiconductor materials such as silicon, amorphous silicon, SiC,SiGe, Ge, GaN, GaP, GaAs and organic semiconductors; phase-changematerials such as GeSbTe; inorganic conductive materials such as ITO;and polymer resin materials such as polyimide-based,polybenzooxazole-based, acrylic, epoxy-based and phenol-based materials.

The polishing agent, polishing agent set and polishing method of thisembodiment can be employed not only for polishing of film-likematerials, but also for various types of substrates made of glass,silicon, SiC, SiGe, Ge, GaN, GaP, GaAs, sapphire or plastics.

The polishing agent, polishing agent set and polishing method of thisembodiment can be employed not only for production of semiconductorelements, but also for production of image display devices such as TFTsand organic ELs; optical parts such as photomasks, lenses, prisms,optical fibers and single crystal scintillators; optical elements suchas optical switching elements and optical waveguides; light-emittingelements such as solid lasers and blue laser LEDs; and magnetic storagedevices such as magnetic disks and magnetic heads.

EXAMPLES

The present invention will now be explained in detail by examples, withthe understanding that the invention is not limited to the examples.

<Synthesis of Hydroxide of a Tetravalent Metal Element>

175 g of Ce(NH₄)₂(NO₃)₆ was dissolved in 8000 g of purified water toobtain a solution. Next, while stirring the solution, 750 g of anaqueous imidazole solution (10 mass % aqueous solution, 1.47 mol/L) wasadded dropwise at a mixing rate of 5 mL/min to obtain a dispersion(yellowish white) containing 29 g of particles of hydroxide of cerium.The particles of hydroxide of cerium were synthesized at a temperatureof 25° C. and a stirring speed of 400 min⁻¹. The stirring was carriedout using a 3-blade pitch paddle with a total blade section length of 5cm.

The obtained dispersion of particles of hydroxide of cerium wassubjected to solid-liquid separation by centrifugal separation (4000min⁻¹, 5 minutes), and a precipitate at a solid content of approximately10% was taken out. Water was mixed with the precipitate obtained bysolid-liquid separation so that a cerium hydroxide content was adjustedto 1.0 mass %, and an ultrasonic cleaner was used to disperse theparticles in the water to prepare a cerium hydroxide slurry storagesolution.

<Measurement of Mean Particle Diameter>

Upon measurement of the mean particle diameter of the particles ofhydroxide of cerium in the cerium hydroxide slurry storage solutionusing an N5, trade name of Beckman Coulter, Inc., a value of 25 nm wasobtained. The measuring method was as follows. First, approximately 1 mLof measuring sample (aqueous dispersion) containing 1.0 mass % ofparticles of hydroxide of cerium was placed in a 1 cm-square cell, andthe cell was set in the N5. Measurement was performed at 25° C. with therefractive index of the measuring sample adjusted to 1.333 and theviscosity of the measuring sample adjusted to 0.887 mPa·s, and the valueindicated as Unimodal Size Mean was read off.

<Structural Analysis of Abrasive Grains>

A suitable amount of the cerium hydroxide slurry storage solution wastaken and vacuum dried to isolate the abrasive grains, and thenthoroughly washed with purified water to obtain a sample. The obtainedsample was measured by FT-IR ATR, and a peak for nitrate ion (NO₃ ⁻) wasobserved in addition to a peak for hydroxide ion (OH⁻). The same samplewas measured by XPS(N—XPS) for nitrogen, and a peak for nitrate ion wasobserved while no peak for NH₄ ⁺ was observed. These results confirmedthat the abrasive grains in the cerium hydroxide slurry storage solutionat least partially contain particles having nitrate ion bonded to ceriumelement. Also, since it also at least partially contains particleshaving hydroxide ion bonded to cerium element, this confirmed that theabrasive grains contained hydroxide of cerium.

<Measurement of Absorbance and Light Transmittance>

A suitable amount of cerium hydroxide slurry storage solution was takenand diluted with water so that an abrasive grain content was adjusted to0.0065 mass % (65 ppm), to obtain a measuring sample (aqueousdispersion). Approximately 4 mL of this measuring sample was placed in a1 cm-square cell, and the cell was set in a spectrophotometer (apparatusname: U3310) by Hitachi, Ltd. Spectrophotometry was performed in awavelength range of 200 to 600 nm to measure the absorbance for lightwith a wavelength of 290 nm and absorbance for light with a wavelengthof 450 to 600 nm. The absorbance for light with a wavelength of 290 nmwas 1.192, and the absorbance for light with a wavelength of 450 to 600nm was less than 0.010.

Approximately 4 mL of the cerium hydroxide slurry storage solution(particle content: 1.0 mass %) was placed in a 1 cm-square cell, and thecell was set in a spectrophotometer (apparatus name: U3310) by Hitachi,Ltd. Spectrophotometry was performed in a wavelength range of 200 to 600nm to measure the absorbance for light with a wavelength of 400 nm andthe light transmittance for light with a wavelength of 500 nm. Theabsorbance for light with a wavelength of 400 nm was 2.25, and the lighttransmittance for light with a wavelength of 500 nm was 92%/cm.

<Preparation of CMP Polishing Agent>

The CMP polishing agents used in Examples 1 to 8 and ComparativeExamples 1 to 7 were prepared so as to comprise 0.05 mass % of particlesof hydroxide of cerium as the abrasive grains, 0 to 0.5 mass % of theadditives listed in Table 1, 0.005 mass % of imidazole as a pH regulatorand purified water as the remainder, based on the total mass of the CMPpolishing agent. After dissolving the components other than the abrasivegrains in the purified water, the cerium hydroxide slurry storagesolution was mixed and stirred to prepare a CMP polishing agent.

The additives used in the examples were compounds having the followingstructures.

Polyglycerin tetramer: Compound satisfying the formula (I) (m=4)

Polyglycerin hexamer: Compound satisfying the formula (I) (m=6)

Polyglycerin decamer: Compound satisfying the formula (I) (m=10)

Polyglycerin icosamer: Compound satisfying the formula (I) (m=20)

SC-E450 (diglycerin polyether (polyoxyethylene diglyceryl ether) bySakamoto Yakuhin Kogyo Co., Ltd., compound satisfying the formula (II)(R¹: group represented by the formula (III), R²: hydrogen atom, R³:hydrogen atom, n=2, p=6)

SC-E2000 (diglycerin polyether (polyoxyethylene diglyceryl ether) bySakamoto Yakuhin Kogyo Co., Ltd., compound satisfying the formula (II)(R¹: group represented by the formula (III), R²: hydrogen atom, R³:hydrogen atom, n=2, p=40)

SC-E4500 (diglycerin polyether (polyoxyethylene diglyceryl ether) bySakamoto Yakuhin Kogyo Co., Ltd., compound satisfying the formula (II)(R¹: group represented by the formula (III), R²: hydrogen atom, R³:hydrogen atom, n=2, p=90)

<Evaluation of Liquid Properties>

The pH of the CMP polishing agent and the mean particle diameter of theparticles of hydroxide of cerium in the CMP polishing agent wereevaluated under the following conditions. For Examples 1 to 8 andComparative Examples 1 to 7, the pH of the CMP polishing agent was 6.5and the mean particle diameter of the particles of hydroxide of ceriumwas 25 nm.

(pH)

Measuring temperature: 25±5° C.

Measuring apparatus: Model PHL-40 by DKK Corp.

Measuring method: After 2-point calibration using standard buffersolution (phthalate pH buffer solution: pH: 4.01 (25° C.), neutralphosphate pH buffer solution: pH 6.86 (25° C.)), the electrode wasplaced in the CMP polishing agent, and then the pH was measured with themeasuring apparatus described above after at least 2 minutes passed forstabilization.

(Mean Particle Diameter of Particles of Hydroxide of Cerium)

The mean particle diameter of the particles of hydroxide of cerium inthe CMP polishing agent was measured using an N5, trade name of BeckmanCoulter, Inc. The measuring method was as follows. First, approximately1 μL of the CMP polishing agent was placed in a 1 cm-square cell and thecell was set in the N5. Measurement was performed at 25° C. with therefractive index of the measuring sample adjusted to 1.333 and theviscosity of the measuring sample adjusted to 0.887 mPa·s, and the valueindicated as Unimodal Size Mean was read off.

<CMP Polishing Conditions>

The CMP polishing agent was used for polishing of substrates to bepolished, under the following polishing conditions. A substrate having apolysilicon film was polished in each of Examples 1 to 8 and ComparativeExamples 1 and 7. In each of Comparative Examples 2 to 6, the substratehaving a polysilicon film was not polished due to the low silicon oxidefilm polishing rate.

(Polishing Conditions)

Polishing apparatus: Reflexion (Applied Materials, Inc.)

CMP polishing agent flow rate: 200 mL/min

Substrates to be polished: A substrate having a 1 μm-thick silicon oxidefilm formed on a silicon substrate by plasma CVD method, and a substratehaving a 0.2 μm-thick polysilicon film formed on a silicon substrate byCVD method.

Abrasive pad: Foamed polyurethane resin with closed cells (Model IC1000, Rohm & Haas, Japan).

Polishing pressure: 14.7 kPa (2 psi)

Relative speed between substrate and polishing platen: 85 m/min

Polishing time: 1 minute

Cleaning: CMP treatment was followed by cleaning with ultrasonic waterand drying with a spin dryer.

<Evaluation of Polished Products>

The polishing rates for films to be polished (silicon oxide film andpolysilicon film) that had been polished and cleaned under theconditions described above (silicon oxide polishing rate: SiO₂RR,polysilicon polishing rate: p-SiRR) were determined by the followingformula. The difference in film thickness of the film to be polishedbefore and after polishing was determined using a light-interferencefilm thickness meter (trade name: F80 by Filmetrics Japan, Inc.).(Polishing rate: RR)=(Film thickness difference of film to be polishedbefore and after polishing (nm))/polishing time (min))

Also, a polished substrate (blanket wafer substrate having a siliconoxide film) that had been polished and cleaned under the conditionsdescribed above was dipped for 15 seconds in an aqueous solution of 0.5mass % hydrogen fluoride and washed with water for 60 seconds. Next, thesurface of the polished film was cleaned for 1 minute using a polyvinylalcohol brush while supplying water, and was dried. Complus by AppliedMaterials, Inc. was used to detect defects of 0.2 μm or greater on thesurface of the polished film. Also, upon observation of the surface ofthe polished film using the defect detection coordinates obtained by theComplus, and using an SEM Vision by Applied Materials, Inc., the numberof polishing scratches of 0.2 μm or greater at the surface of thepolished film was about 0 to 3 (per wafer) in both the examples and thecomparative examples, indicating that generation of polishing scratcheswas adequately inhibited.

Table 1 shows the silicon oxide polishing rate (SIO₂RR), the polysiliconpolishing rate (p-SiRR), the polishing selectivity ratio, i.e. siliconoxide polishing rate/polysilicon polishing rate, and the like, forExamples 1 to 8 and Comparative Examples 1 to 7. The HLB value of theadditives of Examples 1 to 8 was 20.0. The polyglycerol fatty acid esterof Comparative Example 7 (polyglycerin mean polymerization degree: 4,the HLB value: 12.2) is not a compound represented by formula (I) or(II), since it is a fatty acid ester.

TABLE 1 Polishing Weight- selectivity average SiO₂RR p-SiRR ratioAdditive molecular (nm/ (nm/ (SiO₂RR/ (mass %) weight min) min) p-SiRR)Example 1 Polyglycerin 300 200 19 11 tetramer (0.5) Example 2Polyglycerin 420 225 21 11 hexamer (0.5) Example 3 Polyglycerin 680 28024 12 decamer (0.5) Example 4 Polyglycerin 1300 315 22 14 icosamer (0.5)Example 5 SC-E450 450 230 17 14 (0.5) Example 6 SC-E2000 2000 210 15 14(0.5) Example 7 SC-E4500 4500 195 16 12 (0.5) Example 8 Polyglycerin1300 270 23 12 icosamer (0.05) Comparative None — 160 100 1.6 Example 1Comparative Glycerin 92 115 — — Example 2 (0.05) Comparative Diglycerin166 165 — — Example 3 (0.05) Comparative Polyvinyl 10000 180 — — Example4 alcohol (0.05) Comparative α-cyclodextrin 972 180 — — Example 5 (0.05)Comparative Polyoxy- 346 130 — — Example 6 ethylene sorbitan monolaurate(0.05) Comparative Polyglycerin 492 162 23 7.0 Example 7 fatty acidester (0.05)

The results shown in Table 1 will now be explained in greater detail.For preparation of the CMP polishing agent in Example 1, a polyglycerintetramer (weight-average molecular weight: 300) was used at 0.5 mass %.For Example 1, the silicon oxide polishing rate was 200 nm/min, whichwas a higher value than Comparative Examples 1 to 7. Also, the polishingselectivity ratio was 11, which was a higher value than ComparativeExamples 1 and 7.

For preparation of the CMP polishing agent in Example 2, a polyglycerinhexamer (weight-average molecular weight: 420) was used at 0.5 mass %.For Example 2, the silicon oxide polishing rate was 225 nm/min, whichwas a higher value than Comparative Examples 1 to 7. Also, the polishingselectivity ratio was 11, which was a higher value than ComparativeExamples 1 and 7.

For preparation of the CMP polishing agent in Example 3, a polyglycerindecamer (weight-average molecular weight: 680) was used at 0.5 mass %.For Example 3, the silicon oxide polishing rate was 280 nm/min, whichwas a higher value than Comparative Examples 1 to 7. Also, the polishingselectivity ratio was 12, which was a higher value than ComparativeExamples 1 and 7.

For preparation of the CMP polishing agent in Example 4, a polyglycerinicosamer (weight-average molecular weight: 1300) was used at 0.5 mass %.For Example 4, the silicon oxide polishing rate was 315 nm/min, whichwas a higher value than Comparative Examples 1 to 7. Also, the polishingselectivity ratio was 14, which was a higher value than ComparativeExamples 1 and 7.

For preparation of the CMP polishing agent in Example 5, SC-E450(diglycerin polyether (polyoxyethylene diglyceryl ether) by SakamotoYakuhin Kogyo Co., Ltd., weight-average molecular weight: 450) was usedat 0.5 mass %. For Example 5, the silicon oxide polishing rate was 230nm/min, which was a higher value than Comparative Examples 1 to 7. Also,the polishing selectivity ratio was 14, which was a higher value thanComparative Examples 1 and 7.

For preparation of the CMP polishing agent in Example 6, SC-E2000(diglycerin polyether (polyoxyethylene diglyceryl ether) by SakamotoYakuhin Kogyo Co., Ltd., weight-average molecular weight: 2000) was usedat 0.5 mass %. For Example 6, the silicon oxide polishing rate was 210nm/min, which was a higher value than Comparative Examples 1 to 7. Also,the polishing selectivity ratio was 14, which was a higher value thanComparative Examples 1 and 7.

For preparation of the CMP polishing agent in Example 7, SC-E4500(diglycerin polyether (polyoxyethylene diglyceryl ether) by SakamotoYakuhin Kogyo Co., Ltd., weight-average molecular weight: 4500) was usedat 0.5 mass %. For Example 7, the silicon oxide polishing rate was 195nm/min, which was a higher value than Comparative Examples 1 to 7. Also,the polishing selectivity ratio was 12, which was a higher value thanComparative Examples 1 and 7.

For preparation of the CMP polishing agent in Example 8, a polyglycerinicosamer (weight-average molecular weight: 1300) was used at 0.05 mass%. For Example 8, the silicon oxide polishing rate was 270 nm/min, whichwas a higher value than Comparative Examples 1 to 7. Also, the polishingselectivity ratio was 12, which was a higher value than ComparativeExamples 1 and 7.

INDUSTRIAL APPLICABILITY

According to the invention, it is possible to provide a polishing agent,a polishing agent set and a polishing method that can increase thepolishing rate for insulating materials and that can also improve thepolishing selectivity for insulating materials with respect to stoppermaterials. Furthermore, according to the invention, particularly, in CMPtechniques for flattening of STI insulating materials, pre-metalinsulating materials, interlayer insulating materials and the like, itis possible to provide a polishing agent, a polishing agent set and apolishing method that can polish the insulating materials at high rateand that can also improve the polishing selectivity for insulatingmaterials with respect to stopper materials. In addition, according tothe invention, it is possible to allow the polishing of insulatingmaterials with low polishing scratches while also increasing thepolishing rate for insulating materials.

The invention claimed is:
 1. A polishing agent comprising: water, anabrasive grain containing a hydroxide of a tetravalent metal element,and a glycerin compound, the glycerin compound being at least onecompound represented by general formula (II) below:

wherein, in formula (II), n represents an integer of 2 or greater, andR¹, R² and multiple R³ each independently represent hydrogen atom, agroup represented by general formula (III) below or a group representedby general formula (IV) below; and wherein the case where R¹, R² andmultiple R³ are all hydrogen atom is excluded;

wherein, in formula (III), p represents an integer of 1 or greater

and wherein, in formula (IV), q represents an integer of 1 or greater.2. The polishing agent according to claim 1, wherein the hydroxide of atetravalent metal element is at least one selected from the groupconsisting of hydroxide of rare earth metal element and hydroxide ofzirconium.
 3. The polishing agent according to claim 1, wherein a meanparticle diameter of the abrasive grain is 1 nm or greater and 300 nm orless.
 4. The polishing agent according to claim 1, wherein a content ofthe abrasive grain is 0.005 mass % or greater and 20 mass % or lessbased on a total mass of the polishing agent.
 5. The polishing agentaccording to claim 1, wherein a weight-average molecular weight of theglycerin compound is 250 or greater and 10×10³ or less.
 6. The polishingagent according to claim 1, wherein a content of the glycerin compoundis 0.01 mass % or greater and 10 mass % or less based on a total mass ofthe polishing agent.
 7. The polishing agent according to claim 1,wherein a pH is 3.0 or greater and 12.0 or less.
 8. The polishing agentaccording to claim 1, used for polishing of a surface to be polishedcontaining silicon oxide.
 9. A polishing agent set comprisingconstituent components of the polishing agent according to claim 1separately stored as a first liquid and a second liquid, the firstliquid containing the abrasive grain and water, and the second liquidcontaining the glycerin compound and water.
 10. A polishing method for abase substrate, comprising a step of polishing a surface to be polishedof a base substrate using the polishing agent according to claim
 1. 11.A polishing method for a base substrate, comprising a step of polishinga surface to be polished of a base substrate using a polishing agentobtained by mixing the first liquid and the second liquid of thepolishing agent set according to claim
 9. 12. A polishing method for abase substrate having an insulating material and polysilicon, thepolishing method comprising a step of selectively polishing theinsulating material with respect to the polysilicon using the polishingagent according to claim
 1. 13. A polishing method for a base substratehaving an insulating material and polysilicon, the polishing methodcomprising a step of selectively polishing the insulating material withrespect to the polysilicon using a polishing agent obtained by mixingthe first liquid and the second liquid of the polishing agent setaccording to claim 9.